Using a treatment referred to as photodynamic therapy (PDT), light can be used to destroy abnormal tissue in tumors and pathogenic organisms. Before administering PDT, an appropriate photoreactive agent is infused into the tissue at a treatment site or is applied to the organisms intended to be destroyed; the abnormal tissue or organisms absorb this agent to a much greater extent than surrounding normal tissue. Photoreactive agents have a characteristic light absorption waveband and react when exposed to light within that waveband by releasing free radicals and other chemicals. When a light source producing light having the absorption waveband of the photoreactive agent is directed at the treatment site, the abnormal tissue or disease organisms at the treatment site are destroyed by the chemicals produced by the photoreactive agent.
Typically, an external laser light source is used to administer PDT to a treatment site on the skin of a patient or at an internal treatment site that is surgically exposed. Alternatively, the light from the source may be conveyed to an internal treatment site such as a tumor through one or more optical fibers. Commonly assigned U.S. Pat. No. 5,445,608 discloses several different embodiments for providing PDT using transcutaneously implantable light source probes that include a plurality of relatively low intensity light sources, such as light emitting diodes (LEDs). It has been shown that relatively low intensity light administered for an extended period of time can be even more effective in PDT than high intensity light administered for a short period of time. Thus, the light source probes disclosed in the above-referenced patent are intended to be implanted and left in place at an internal treatment site to effect PDT over an extended time.
A commonly assigned U.S. patent application, Ser. No. 08/613,390, entitled "Flexible Microcircuits for Internal Light Therapy," filed on Mar. 7, 1996, discloses a number of flexible probes, each of which include a flexible substrate on which are disposed conductive traces electrically connected to leads through which electrical current is conveyed from a power source (implanted or external). A plurality of light sources are connected to the conductive traces and are mounted on the flexible substrate. A transparent, biocompatible polymer envelope encloses the flexible circuit and light sources, providing protection for the components as the flexible probe is advanced within the patient's body. This reference teaches that a flexible probe can readily be bent, folded, or rolled, thereby enabling the probe to pass through a guide tube, an incision, a catheter, or a lumen of relatively small diameter, to facilitate disposition of the probe at an internal treatment site. Once inserted at the internal treatment site, a folded or rolled flexible probe can be unfolded or unrolled to supply light for PDT or to implement other types of medical treatment. One of the embodiments disclosed in this reference is a flexible grid on which the plurality of light sources are disposed in a spaced-apart array. The reference teaches that the flexible grid can be conformed to a treatment site, e.g., wrapped around a tumor or a blood vessel. However, the reference does not disclose any means for shifting the light sources relative to the flexible substrate of the grid or for modifying the distribution of the light sources relative to the probe and its disposition at the treatment site. Clearly, it would be desirable to provide a mechanism enabling the configuration of light sources in an array to be adjusted, to optimize the pattern in which light is delivered to the treatment site. For example, many tumors have an irregular surface and are of varying thickness. A greater light intensity irradiating the thicker portion of the tumor relative to that irradiating the thinner portion would be required for optimum results. Thus, to treat such tumors, it would be preferable to configure a plurality of light sources at the treatment site, so that light is delivered to the tumor in a non-uniform distribution, with relatively more light being delivered to the thicker portions of the tumor than to the thinner portions. Furthermore, treatment sites having irregular surfaces could more effectively be treated with an array in which the position of the light source probes is adjustable at the treatment site than with an array in which the light sources or probes are in a fixed position.
Unless a treatment site is surgically exposed, configuring light sources after a probe has been implanted so as to irradiate a specific treatment site with light in a non-uniform distribution, would likely be done endoscopically. A flexible substrate grid on which light sources are mounted in fixed positions, as disclosed in the second reference discussed above, does not permit the configuration of light sources or probes to be altered once the grid is located at the treatment site within the patient's body. No currently available implantable array or probe provides the required flexibility in configuration. Accordingly, a different type of flexible array is needed that enables the location of light sources or probes comprising an array to be altered after the array is implanted inside a patient's body.